SR20DET "Timing Scatter"

[Solo_S14]

So this might not be the proper term, but I'm looking for some help in fixing a timing issue. I spoke with a local tuner last week, and this is what he described, so I figured I'd roll with the term, and try to get this thing fixed.

Anyone who's been following my build thread will know that I've had a number of engine troubles over the past year or two. I'm starting again with a fresh engine, and want to finally get this thing running properly.

My tuner described an issue that he's seen with the AEM EMS that's caused by the apparent low resolution of the software, not being able to keep up with the SR20DET igniter/ CAS count. The issue that he's seen is best described as timing staying solid until you get higher in the rpm range, then the software can't keep up and timing basically goes out the window, jumping around everywhere.

My issue is not the same as this, what I've seen is a little more manageable. I can set my timing to 15deg at idle, and it's fine. Once I hit 1500ish RPM my timing jumps up into the 25ish (I'm guessing) range or more! This is with all of my tables set to 15 deg across the entire map.

I am able to set timing at idle to a jumpy 6-8deg somewhere, and when I rev the engine past 1500rpm and into the 6000rpm range (standing still) the timing sits solid at 15deg.

So basically it looks like I'm gaining 7-8 deg or more when moving from idle to operating range using this one test. Does anyone have any suggestions or any info about my problem? I don't think it's an AEM issue, as I can get the timing to stay at 15deg through higher rpm, I just have the issue of setting my timing at idle now??? Timing is measured with a plug wire between coil #1 and plug #1, with an adjustable timing light set at ZERO degrees. Crank pulley is reading 15deg with tables at 15deg.

[Solo_S14]

To give an indication of the problems that I'm having, I'll post up my original tune that a previous motor ran on fine, then I'll post up the tune that I'm running now to keep the engine from detonating as soon as I build any boost:

Note: Base timing was set properly, piston #1 at TDC, Intake / Exhaust cams at 10/1 ish (IIRC) with lobes facing away from each other, 20 (10) links between teeth.


1) Previous Tune (380 whp on previous engine, detonating death on current)






2) Current (Safe / No Power) Tune






Obviously I'm pulling up to 20deg in higher rpm, which is also extra safe, so could account for the jump in timing. I just need to figure out this issue, then I can book some dyno time again and clean up the tune.

[Def]

For how much timing you run in the midrange you ramp it in too quickly at high RPM.

Honestly, the timing looks really conservative in the first tune except for the last few RPM cells. You sure your base timing was set properly? What did it do when you added a degree or took away a degree on the dyno?

[Solo_S14]

The first tune was the tune that I got with the car when I bought it. Those guys did the tune for a magazine spread, and apparently hit the dyno a few times over the span of a month to get it "dialed in". I guess that it's possible that base timing was set inproperly during that tune, which would explain the apparent conservative nature of the tune over the map. Although it doesn't explain why they have 15 degrees in the idle cells, you would assume that they used this to set timing to 15deg prior to tuning.

I think the real issue that I'm having is the initial "jump" in timing as soon as I get on the gas / pass 1200ish rpm. I can set timing at IDLE to 15 degrees, and it jumps into the 25ish range as soon as I rev the engine (with all cells set to 15). I proved the jump by setting timing at IDLE to ~6degrees, and it jumps to 15 degrees and stays at 15 for the entire map when using my "all 15 degrees map". i.e. to test this I changed every cell to 15 degrees, and can hit it in high rpm after the inital jump.

A few guys have told me that the tune looks conservative in the mid to high range in the past, so I'm sure you're correct in saying that Def. However, I think the main issue is the initial jump in timing from idle to 1200rpm+........if I can get that figured out, I can work out a tune using that first tune as a base map. I just can't understand what would cause an approximately 10degree jump at approximately 1200rpm, then stay steady/normal until redline?

I guess that realistically I could just tune to the issue and set timing to the 6deg at idle (when 15 is in the cell), so that I can hit the 15degrees throughout the map. This will give me a steady base to work from for 1200rpm +. From here I could tune the AEM to add timing during idle to equal 15 (so 24 in the cell), then carry on tuning the map as per usual.

Do you think that VTC is causing me any issues? Not really sure how that system works with the standalone, or the rpm range that it works in, but maybe it's throwing timing off in the low rpm range, which would explain why timing is predictable after 1200?

[Solo_S14]

This was apparently the pull using that map.

[Tower240sx]

there are a couple how to's and a note about buying a new reluctor wheel from AEM if probles persist attempting to set timing with a nissan cas/dizzy (they use the same wheel and pickup)

Try This

[Def]

Notice how the torque AND HP jump up as the timing really really ramps in past ~6.5k. If the timing wasn't super super conservative before that point, it's going to knock its ass off if you put that much timing in.

I don't like how much smoothing Dynapak dynos have, it's really hard to see how smooth the power delivery is.

[Solo_S14]

I see what you're saying Def and yeah I agree.
However, I begin to knock as soon as I get on the gas / get into boost / under load conditions. I mean like 2500rpm as a ballpark.

I've also been able to observe a ~10deg timing jump between the 800rpm idle and ~1200 rpm range, with the entire timing map set to 15deg, sitting in my garage under no load conditions. I agree that the previous tune is not ideal, however the timing jump that I'm describing is happening irregardless of the tune that I load onto the ECU.

Tower240SX, it sounds like a few of those guys describe the issue that my tuner was talking about, with timing going out the window in high rpm. When I get another day off sometime I can check out some more of the settings, and troll the aem forums a little more. Thanks for the link, maybe it will get me a little closer to finding out the cause of this stupid problem.

[Def]

Do you have TPS dot ignition advance in the AEM? Sounds like that's what you're seeing.

[Solo_S14]

Not that I know of, but I can check it out. Makes sense that as soon as the TPS voltage rises, it could trigger an advance. I guess the dumb way to test it would be to unplug the TPS and see if it makes any difference, but I don't think that I have this option.

[Tower240sx]

zero out your knock ign retard maps,
make sure the egt ign retard isn't enabled,
veryify you don't have a boost ign retard feature enabled,

there are far too many ways to retard timing in the AEM, the map is just the "base" timing from what I can tell (I read the manual the other day)

[Colorado S14]

How is the timing calculated when I see a -8? Standard SR timing then that -8 would be the retard?

[Solo_S14]

That -8 in reality should be more like +10 if I didn't have the jumping/detonating issue.
In this case, base is 15 and that cell is telling the AEM to fire 23 degrees after this i.e. 8 deg ATDC (If I understand the tables correctly). The previous tune would have told that cell to fire 10deg BTDC.

I guess to properly answer your question, yeah that cell is reading an 8 degree retard instead of a 10 degree advance in the "safe tune".